1. Field of the Invention
The present invention relates to a plasma processing apparatus for generating a uniform strip-shaped plasma, and more particularly, to a plasma processing apparatus for performing a plasma process such as a chemical vapor deposition (CVD) process, an ashing process, a sputtering process, an etching process or the like by projecting a generated plasma onto an object to be processed, wherein the plasma is generated by supplying a microwave within a plasma chamber in which a predetermined processing gas is contained at a predetermined pressure.
2. Description of the Related Art
Conventionally, a method of forming a diamond film on a mechanical tool, a magnetic film or the like as a protection film has been developed, and in the conventional method, a plasma is used in order to form the protection film uniformly in a high speed at a low temperature. Further, conventionally, a plasma has been used upon etching a film in one of processes for manufacturing an LSI and a liquid crystal display unit.
FIG. 18 shows the whole composition of a conventional plasma processing apparatus.
Referring to FIG. 18, the conventional plasma processing apparatus comprises a microwave generator 1, an isolator 2, a directional coupler 3, an impedance matching unit 4, a corner rectangular waveguide 5, rectangular waveguides 6 and 7, and a terminating unit 8 including a movable short-circuit plate 8a which are connected in series to each other, and further comprises a silica tube 9 mounted so as to pass through a through hole formed in the rectangular waveguide 7. The silica tube 9 is connected to a vacuum pump (not shown). After the vacuum pump makes the inner air of the silica tube 9 in a predetermined high vacuum state, and then a predetermined processing gas G is supplied into the silica tube 9 so that the inner pressure of the silica tube 9 becomes a predetermined pressure.
A microwave generated by the microwave generator 1 is supplied through the isolator 2, the directional coupler 3, the impedance matching unit 4, the corner rectangular waveguide 5 and the rectangular waveguide 6 into the rectangular waveguide 7. The microwave supplied within the rectangular waveguide 7 propagates through a tube wall of the silica tube 9 into a plasma chamber located within the silica tube 9, and then makes the processing gas supplied within the silica tube 9 in a plasma state so as to generate a plasma of the processing gas. An object to be processed is provided in the center of the rectangular waveguide 7 located within the silica tube 9 or on the downstream side of the generated plasma so as to be projected by the generated plasma.
Further, a plasma generating apparatus utilizing the Electron Cyclotron Resonance (ECR) (referred to as an ECR plasma generating apparatus hereinafter) has been used. In the ECR plasma generating apparatus, a microwave is supplied into a plasma chamber through a rectangular waveguide, and an air-core coil is provided so as to surround the plasma chamber. A magnetic field generated by exciting the air-core coil and the supplied microwave lead to the ECR phenomenon, thereby generating a plasma having a high density in a high vacuum state.
In order to improve the processing efficiency in performing a plasma process such as a process of forming a thin film, etching a film or the like, it has been necessary to provide a technique or method of performing the plasma process uniformly at a high speed at a low temperature by uniformly projecting a plasma onto an object having a relatively large area to be processed. Further, in a process for manufacturing a liquid crystal display performed in a manner similar to that of the process for manufacturing an LSI, as the size of the liquid crystal display is enlarged, it has been necessary to provide a technique or method of uniformly projecting the generated plasma onto a processing surface having a relatively large area of the object to be processed.
However, in the conventional plasma generating apparatuses, since there is caused a difference of the density of the plasma between the center of the plasma and the periphery thereof, a speed of forming a film and an etching speed at respective different parts of the object to be processed can not be uniform, and then it is difficult to manufacture a device having a good quality with a higher efficiency. Further, since the cross section of the plasma is generated in a shape of circle, the plasma process can not be efficiently performed in the case where the processing surface of the object to be processed has either a rectangular shape or a square shape.
As a method of generating a plasma having a larger diameter or area in the conventional plasma processing apparatus shown in FIG. 15, it is supposed to enlarge the diameter of the silica tube 9. However, since the diameter of the silica tube 9 is limited by the dimension of the waveguide determined depending on the wavelength of the used microwave, the diameter of the silica tube 9 can not be enlarged so as to process an enlarged object to be processed.
Further, in the ECR plasma generating apparatus, in order to enlarge the diameter of the generated plasma, it is necessary to enlarge the diameter of the air-core coil, resulting in enlarging the size of the ECR plasma generating apparatus. This results in that the enlarged ECR plasma generating apparatus can not be used for practical use.